This Competing Continuation Application requests funding for Years 06 to 10 of the NIMH collaborative Multimodal Treatment Study of Children with Attention-Deficit Hyperactivity Disorder (MTA Study). In a parallel-group design, 576 rigorously diagnosed children with ADHD (96 at each of 6 sites), age 7-9, are randomly assigned to four treatment conditions: (1) Medication-only; (2) Psychosocial-only; (3) Combined (medication & psychosocial); or (4) Assessment-and- Referral-only. All but the latter are treated intensively for 14 months, with assessments for all subjects at baseline, 3, 9, 14, and 24 months. The original MTA design thus provides short-term (10 months post- treatment) follow-up at 24 months, but insufficient funds and time prevented longer-term follow-up. This Continuation request, in concert with the companion Competing Supplement for Year 05, would begin the longer-term follow-up of differential treatment effects by following all subjects at least through their 5th year (4 yr post-treatment). Continuation Aim 1 is to conduct confirmatory tests of the hypothesis that a Combined Treatment strategy is significantly more effective in producing long-term therapeutic gains and preventing new psycho pathology than Medication or Psychosocial-treatment alone and that the difference is clinically meaningful. Continuation Aim 2 is to conduct confirmatory tests of the hypothesis that systematic, intensive treatments (all 3 active MTA treatments) are significantly more effective (statistically and clinically) in producing long-term therapeutic gains and preventing new psychopathology than treatments typically received in the community. Continuation Aim 3 is to conduct confirmatory tests of the hypothesis that systematic treatments for ADHD in early childhood alter the risk for subsequent patterns of substance use and abuse and that the risk alteration is clinically significant. Continuation Aim 4 is to conduct exploratory analyses to determine whether pre-treatment individual differences (severity, comorbidity, parent functioning, family history) are associated with patterns of stability/change in treatment effects. Continuation Aim 5 is to conduct exploratory analyses to determine the extent to which patterns of stability/change in therapeutic attitudes or attributions and in treatment-related behaviors vary as a function of randomly assigned treatment, pre- or post-treatment differences in functioning, post- treatment reports of satisfaction, and preexisting characteristics.